Method of increasing hardness of aluminum-silicon composite

ABSTRACT

A method of increasing the hardness of an aluminumsilicon composite comprising aluminum as the principal metal, with silicon, magnesium and copper in substantial amounts, iron, titanium, manganese and zinc in lesser amounts and a substantial amount of a non-metal filler such as zircon, alumina, zirconia or aluminum silicates, wherein the composite is subjected to a three-stage heat treatment comprising a solution heat treatment followed by a first and second precipitation heat treatment.

Sanders et al.

METHOD OF INCREASING HARDNESS OF ALUMINUM-SILICON COMPOSITE Inventors:Robert N. Sanders, Baton Rouge,

La.; Alex R. Valdo, Elgin, Ill.

Assignee: Ethyl Corporation, Richmond, Va.

Filed: July 9, 1973 Appl. No.: 377,724

Related US. Application Data Division of Ser. No. 219,523, Jan. 20,abandoned.

References Cited UNITED STATES PATENTS 9/1934 Pacz 148/159 X 9/1938Schwarz 75/143 X 5/1939 Dix 148/159 [451 Dec. 24, 1974 2,221,526 11/1940Sampson 148/159 2,357,450 9/1944 Bonsack 75/143 X 2,357,451 9/1944Bonsack... 75/143 X 2,357,452 9/1944 Bonsack... 75/143 X 2,793,9495/1957 lmich i 75/135 3,135,633 6/1964 Hornus 148/159 3,600,163 8/1971Badia et al 75/135 Primary ExaminerC. Lovell Attorney, Agent, orFirm-Donald L. Johnson; John F. Sieberth; Paul H. Leonard [57] ABSTRACTA method of increasing the hardness of an aluminumsilicon compositecomprising aluminum as the principal metal, with silicon, magnesium. andcopper in substantial amounts, iron, titanium, manganese and zinc inlesser amounts and a substantial amount of a nonmetal filler such aszircon, alumina, zirconia or aluminum silicates, wherein the compositeis subjected to a three-stage heat treatment comprising a solution heattreatment followed by a first and second precipitation heat treatment.

2 Claims, No Drawings METHOD OF INCREASING HARDNESS OF ALUMINUM-SILICONCOMPOSITE This is a division of application Ser. No. 219,523 filed onJan. 20, i972, now abandoned.

BACKGROUND OF THE INVENTION The present invention is in the generalfield of metallurgy and relates particularly to non-ferrous metallurgy.The invention is especially related to aluminumsilicon alloys.

It has been previously discovered, U.S. Pat. No. 2,793,949, thatinorganic substances may be incorporated in metals to produce acomposite material product. It is taught therein that mixtures of moltenmetals, including aluminum, and a large variety of inert fillers,including alumina, may be smelted together if the nonmetallic materialto be incorporated into the metal is wetted by the molten metal used.The wetting agents chosen are thoseamong substances which are capable oflowering the surface tension between the metals and the materials to beincorporated therein. Such prior art also teaches that to modify thestructural properties of a metal only slight amounts, less than 1percent, say 0.1 percent, of powders or crystal materials should beadded to the metal. On the other hand, when the object is to obtain, forexample, abrasive compositions, the

ratio of hard materials to be mixed with the molten v metal shouldpreferably exceed 50 percent by volume of the composite product and maybe as high as 95 percent. Although a wide variety of metals and fillersare disclosed, no commercial success has apparently been achieved withthe use of any compositions prepared by such process. Also, a number ofthe compositions disclosed in the reference are highly dangerous, beingin fact explosive compositions.

More recently, it has been discovered that a superior aluminum compositecan be prepared from aluminum, an alkaline earth metal reducing agent,such as magnesium, calcium, beryllium, sodium, potassium, rubidium orcesium, and a non-metal filler such as zircon, alumina, zirconia andaluminum silicates. See U.S. Application Ser. No. 210,127 filed Dec. 20,1971, having a common assignee with the instant invention.

It is therefore a primary object of the present invention to provide anew and improved aluminum-silicon alloy and composite which hassufficient strength to perform the required or desired use thereof andwhich is considerably less expensive than presently availablealuminum-silicon alloys, especially aluminum-silicon casting alloys.

The instant invention is particularly adapted for use in the manufactureof articles wherein hardness is a principal requirement. An example ofsuch articles are be varied over a wide range as desired, by appropriatechanges in the composition.

Still another object of the present invention is to pro vide a new anduseful aluminum-silicon composite which is substantially uniform inconstruction.

Other objects and advantages of the invention will become more readilyapparent from a reading of the specification hereinafter.

SUMMARY OF THE INVENTION The invention relates to a new aluminum-siliconalloy and a new article of manufacture, consisting essentially of analuminum-silicon composite containing aluminum as its principal element,an alkaline earth metal or an alkali metal, especially magnesium, insufficient quantity to be an effective reducing agent, and a substantialamount of an inert non-metallic filler such as zircon, alumina, zirconiaand aluminum silicates, and a method of preparing said article whereinthe alloying elements are heated to sufficient temperature to achievegood fluidity and the filler material is stirred therewith withsufficient stirring to distribute the filler throughout the moltenmetal. Other elements of the alloy and composite are copper, iron,titanium, magnesium and zinc.

DESCRIPTION OF THE PREFERRED EMBODIMENT The preferred aluminum-siliconalloy of this invention comprises in percent by weight elements asfollows:

Silicon 19-2! Magnesium 4-8 Copper 2-4 Iron l Maximum Titanium 0.3Maximum Manganese 0.5 Maximum Zinc 0.5 Maximum Aluminum Balance Thecomposite article of the invention comprises three principalingredients, aluminum-silicon alloy, a metal reducing agent for reducingthe surfaces of a non-metallic filler to a metal-like coating, and anonmetallic filler which is not subject to being reduced by aluminummetal and which can be effectively reduced by the metal reducing agent.Aluminum-silicon alloys or aluminum and silicon are the preferredprincipal metals or elements of the alloy composition. Magnesium is thepreferred metal reducing agent with other alkaline earth or alkalimetals such as calcium, beryllium, sodium, potassium, rubidium andcesium, being suitable. The alkali metals have a relatively lowsolubility in aluminum, e.g., sodium is soluble only to about 0.25weight percent at 775C. These alkali metals therefore, although beingsuitable, have somewhat limited use. Preferred non-metallic fillers arezircon and alumina. Zirconia and aluminum silicates are also suitable.

When the composite material or article of this invention comprisesmagnesium and zircon, the magnesium is preferably in an amount by weightof about 2-l0 percent of the liquid phase, with about 4.5 weight percentmagnesium or metal reducing agent required will vary somewhat with theamount of zircon or non-metallic filler in the composite article.Silicon is present in the composite from about 4 to about 25 weightpercent.

The particle size of the filler may vary from about 60 mesh to about 400mesh, U.S. Siever Series, with a particle size of 100/140 mesh producingan excellent product. A filler or filler material of a distribution ofparticle sizes is preferable.

in the most preferred way of preparing or making the composite articleof the present invention, aluminum and all metallic and silicon alloyingelements except magnesium and zinc are heated to a temperaturesufficient to achieve good fluidity, usually about 850Cin a suitablefurnace or crucible. The temperature necessary will vary with theparticular alloying elements selected and the amount of inert filler tobe added. The temperature will range between the melting point and theboiling point of the alloying elements. In general, it is desirable touse as low a temperature as will provide the desired degree of fluidityof the metallic phase.

After the desired temperature has been reached, the magnesium reducingmetal and zinc, if zinc is included, are added to the molten metal oralloy. Stirring is commenced and the zircon filler is added. Althoughthe filler may be added cold, it is preferably preheated to atemperature of about that of the melt. Stirring is continued until thetiller is dispersed throughout the molten metal, usually about fiveminutes. The time of stirring will vary somewhat with the amount offiller added, and in general as short a stirring time as necessary toachieve adequate particle distribution is preferred. Optimally, themixture is stirred until the tiller is substantially equally distributedthroughout the melt.

After mixing or stirring the molten mixture is cast in the form ofingots or other desired shapes.

When using a pre-prepared or standard aluminum-silicon-magnesium alloyas the metallic phase, the alloy is heated to temperature and thenonmetallic filler is added thereafter. The molten mixture is stirredsufficiently to draw the filler into the molten phase.

In another way of carrying out the present invention, all of theingredients of the composite article, except the metal reducing agent,preferably magnesium, are mixed together and heated to temperature.Magnesium is then added and the mixture stirred. Dross is skimmed fromthe molten mixture and the melt is then cast. This procedure reducesdross.

The aluminum composite or article of the instant invention may also beprepared by mixing all of the components of the article, namelyaluminum, silicon and other elements, metal reducing agent, andnon-metallic filler, together, then heating to desired temperature andstirring. The dross is skimmed from the melt and the molten mixture ispoured into a mold and cast into a suitable shape. This procedure ispreferably followed under an argon purge. Such a purge eliminates somedross from forming.

Hardness of the aluminum-silicon composite is in creased by subjectingthe composite to a three-stage heat treatment as follows:

a. conducting a solution heat treatment at 800l000F for about 4 to 24hours followed by a quench;

b. conducting a precipitation heat treatment at 200-3()0F for about 12to 36 hours; and

c. conducting a second precipitation heat treatment at 300400F for about4 to 12 hours.

In order to facilitate understanding of the invention, the followingexamples are illustrative thereof; however, it is understood that theseexamples do not limit the scope of the invention in any fashion.

GENERAL PROCEDURE air quench. On some castings, a second precipitationheat treatment was conducted at 350F for 8 hours. Hardnesswas measuredon the Rockwell Tester after each heat treatment. Solution heattreatments were also conducted on some samples at l,000F for 16 hours.Hardness was also measured after these treatments.

Particle size distribution of the alumina and zircon fillers were asfollows, unless otherwise specified:

Weight Percent Particle Size Alumina Zircon 40/70 0.0 2.2 /100 4.5 19.]IOU/I40 52.5 53.4 /200 19.7 7.2 200/325 l8.2 7.3

EXAMPLE I A sample of a commercially available alloy suitable for use inautomobile engines hereinafter referred to as Alloy A was prepared bymixing 766 parts of Al, parts of Si, 45 parts of Cu, 10 parts of Fe, 5parts of Mg, 2 parts of Ti, 1 part of Mn, and 1 part of Zn. This mixturewas heated under argon at 850C and cast. The cast plug was placed in a600C oven for 8 hours and completely melted. It was cooled, sawed intopieces, remelted at 550C and cast. The alloy had a Rockwell E hardnessof 87.8 t 3.0 (standard deviation). The specimen was given aprecipitation heat treatment at 250F for 24 hours with an air quench,after which it had a Rockwell B hardness of 76.6 i 4.8 (standarddeviation).

EXAMPLE 2 The following were mixed, heated to 850C for 1 hour andstirred for a brief period: 695 parts of A1, parts of Si, 40 parts ofCu, 9 parts of Fe, 62 parts of Mg, 2 parts of Ti, 1 part of Mn, and 1part of Zn. The alloy (Alloy l) was cast and cooled. The Rockwell Ehardness on the resulting casting was 78.5 i l.4 (standard deviation).The specimen was precipitation heat treated at 250F for 24 hours with anair quench. The Rockwell B hardness on the specimen was then 59.3 :t 3.3(standard deviation). The specimen was then given EXAMPLE 3 Repeatingthe two-step precipitation heat treatment from above resulted in aRockwell B value of 63.2 i 12.1 (standard deviation) after the firststep and after the second step, a top side value of 64.2 i 16.9, and a 5bottom (protected) side value of 81.4 i 5.2 were ob- 720 parts of Alloy1 were recovered from Example tained. 2. To this alloy was added 388parts of ground zircon and the mixture was heated to 850C under an argonEXAMPLE 5 purge, then stirred for 5 minutes. The Rockwell B value Aspecimen from Example 3 was given the same soluwas 46.5 i 9.3 (standarddeviation) on the resulting 10 tion heat treatment and quench as inExample 4. The specimen. After 24 hours at 250F, the hardnessinresulting Rockwell Ehardness was 800:3.1 (standard creased to 61.2 i8.3 (standard deviation), and an addeviation), and the usual two stepprecipitation heat ditional 8 hours at 350F resulted in a value of 64.7i treatment resulted in Rockwell B values of 66.2 i 1.2 9.7 (standarddeviation). (standard deviation), and 72.5 i 9.9 (standard deviation).EXAMPLE 4 The results obtained in Examples 2, 3, 4 and 5 are Beginningwith this example, the ceramic crucibles summarized in Table l,hereinafter. This Alloy 1, con were replaced with4inch steel pipes whichwere sealed sisted of, by weight, 69.5% Al, 19.0% Si, 4.0% Cu at one endand given four coats ofCarborundum Fiber- 0.9% Fe, 6.2% Mg, 0.2% Ti,0.1% Mn and 0.1% Zn. frax Coating Cement, Type QF-l80. The stirrer wasThe alloy incorporated 35% zircon filler with no apparsimilarly coated.The charge consisted of 464 parts of ent difficulty. Significantimprovement of alloy isob- A1, 127 parts of Si, 27 parts of Cu, 6 partsof Fe, 41 tained with a two-step precipitation heat treatment. A partsof Mg, 1.3 parts of Ti, 0.6 parts of Mn and 0.6 solution heat treatmentat 925F for one hour followed parts of Zn. This Alloy 1 mixture washeated to 850C by a simple precipitation heat treatment was less effecas usual. 233 parts of ground zircon were stirred in the tive inhardening the alloy samples. The addition of the alloy mixture over a2-minute period, then the stirrer filler did not significantly decreasethe effectiveness of speed was increased and stirring continued for anaddi the two-step precipitation heat treatment. A solution tional 2minutes. Large pieces of undissolved silicon heat treatment at 1,000Ffor 16 hours followed by a were clearly visible in the casting;therefore, it was distwo-step precipitation heat treatment showedpromise carded. 30 of significant improvement. Some high temperature ox-Thirty parts of Cu, 521 parts of A1, 143 parts of Si, idation damage wasindicated, but this can be easily 6.8 parts of Fe, 1.5 parts of Ti, 0.75parts of Mn, and prevented by the use of an inert atmosphere during-the0.75 parts of Zn were mixed together and heated to solution heattreatment. The protected side hardness TABLE 1 Rockwell E PrecipitationHeat Treatment Solution Heat Treatment Hardness Temp.. Time. RockwellBTemp.. Time. RockwellB Tem;p., Time. RockwellE System As Case "F hr.Hardness F Hardness F hr. Hardness Alloy A 87.8 i 3.0 250 24 76.6 r 4.8Alloy 1 78.5 i 1.4 250 24 59.3 r 3.3 350 s 68.3 1 2.0 Alloy 1 -1- 357.Zircon 46.5 i 9.3"" 250 24 61.2 i 3.3 350 s 64.7 1 9.7 250 24 61.2 i 1.2350 8 72.5 i 9.9" 1000 16 80.0 i 3.1 A1|6 1 Zircon 76.1i1.1 250 24 90.8i 0.9 350 s 67.5 :t 1.7 4 250 72 63.2 :t 12.1 350 8 2 4.2 2 16 .952 100016 84.9 i 7.4

"Rockwell B Hardness ""Sume specimen "Top side value ""Botlom side value850C in the usual way. After 30 minutes, the stirrer was submerged and46.5 partsof Mg were added. After 5 minutes of stirring, the stirrer wasremoved, and then resubmerged after 10 minutes. After 5 minutes hadpassed, 350 parts of ground zircon were stirred in the x e T c @992 intttte est trsr. speed increased and stirring continued until a total of5 minutes had elapsed. The Rockwell E hardness value was 11.: 1.1.1 (seaarq9eviat 2 eftetzthqatsat 250F the hardness value had increased to 90.8i 0.9 (standard deviation). The specimen was then heated to 350F for 8hours with the result that the hardness increased to 67.5 i 1.7(standard deviation) on the Rockwell B scale.

A solution heat treatment at 1,000F for 16 hours was then given and thespecimen water quenched. The Rockwell E value was 84.9 i 7.4 (standarddeviation).

value of 81.4 i- 5.2 compares very favorably with the hardness of 76.6 i4.8 obtained for Alloy A.

EXAMPLE 6 An alloy was prepared to simulate one which would be obtainedby using primary reduction alloy as the silicon source, 353 parts ofa60% Al, 35% Si, 3% Fe, 2% Ti alloy were mixed with 231 parts of Al, 26parts of Cu, 0.5 part of Zn, and 0.5 part of Mn and heated to 850C asusual. After 1 hour at temperature, 39 parts of Mg were added and after5 minutes stirred for 2 minutes. After an additional 18 minutes, 350parts of ground zircon were stirred in the alloy with a gradual increasein stirring speed until a total of 5 minutes has elapsed. The productwas much too viscous to pour.

EXAMPLE 7 parts of powdered silicon, 39 parts of Mg, 26

EXAMPLE 8 Example 7 repeated using lump Si in place of powdered Si.After successful casting and the above series of heat treatments, theRockwell B values, with standard deviation were in order: 96.3 i 4.4;94.0 i 8.0; 94.0 i 6.0; 99.6 i 4.0; and finally 100.4 i 3.9.

EXAMPLE 9 Exactly the same procedure as in Example 8 was followed exceptthat alumina was used in place of zircon. The material could be pouredbut was too viscous to fill the mold well. As cast, it had a Rockwell Bvalue with standard deviation of 70.3 i 1.9, and after 5 days of naturalaging it increased to 81.6 i 5.8.

EXAMPLE 10 The procedures of Example 9 were repeated except A1 0 wasused in place of An excellent casting was obtained.

EXAMPLE 11 The following were mixed and heated to 850C in the usual way:465 parts of A1, 124 parts of Si (powdered), 13 parts of Cu, 5.6 partsof Fe, parts of Mg, 1.0 part of Ti, 07 part of Mn, 0.7 part of Zn. After1 hour at temperature, 350 parts of ground zircon were stirred in asabove with the same results as in Example 7. The example was repeatedexcept that lump Si was used in place of powdered Si and the Mg was notadded until just before the ground zircon. In this case, a fluid systemresulted. A specimen was cast and cooled. The specimen had a Rockwell Bhardness of 82.8 i 12.2 (standard deviation). Regular solution andtwo-stage precipitation heat treatments were given except a nitrogenpurge was used during the solution treatment and 72 hours elapsedbetween solution and precipitation heat treatments. The resultingRockwell B values with standard deviation were 84.0 i 8.8; 91.0 i 12.6;85.0 1*: 11.3; and 90.4 i 5.2, respectively.

EXAMPLE 12 Normal heating and mixing procedures were used with 330 partsof A1, 110 parts of Si, 22 parts of Cu, 55 parts of Zn, 33 parts of Mgand 450 parts of ground zircon. The mixture was too viscous to pour.Repeating the example with 360 parts of Al, 120 parts of Si, 24 parts ofCu, 36 parts of Mg, 60 parts of Zn, and 400 parts of ground zircon gaveresults similar to those obtained in Example 9 on castability. As cast,the Rockwell B value was 89.4 i 4.1, after solution treating 88.9 i 6.7,and precipitation heat treatments gave Rockwell EXAMPLE 13 420 parts ofaluminum, 140 parts of Si and 28 parts of Cu were mixed and heated to850C under an argon purge, the stirrer was submerged and parts of Zn and42 parts of Mg were added. The tensile specimen mold was heated to 850Cand the other two molds to 670C. Using usual stirring procedure, 300parts of zircon were stirred in, then a C1 purge given and the ladleused to fill the molds. The molds did not fill well and there were largequantities of unincorporated powder, excessive deterioration of thestirrer was also noted.

The above example was repeated using a new stirrer and a new steeltensile specimen mold. Flame was noted during the addition of the zircon(a newly composited and ground sample was being-used). The tensilespecimen was broken in the constricted region. The Rockwell B hardnessvalue was 92.5 i 4.1. After 16 hours at 1,000F under purge followed by awater quench, the Rockwell B hardness value was 84.0 t 4.0. The usualtwo-stage precipitation heat treatments gave 85.7 i 4.8, and 87.0 i 3.2,respectively. The above example was again repeated except that notensile specimen was poured, the liquid was poured rather than ladled,and the hardness mold was coated with one coat of Fiberfrax cement andmaintained at 500C. Flaming was again noted. After casting and cooling,the Rockwell E value was 89.0:22. Repeating the above except a 1-hoursoak at temperature before the stirrer was submerged, again resulted inflaming. As cast, solution heat treated, and two-step precipitationtreatments gave, in order, Rockwell B values of 60.8 i 11.3; 55.9 i 9.9;63.9 8 .9 and 78.6 i 2.4

changing roeduie', 420 parts of A1, parts of Si, and 28 parts of Cu weremixed and heated to temperature and maintained for 1 hour with normalstirring every 10 minutes. The stirrer was submerged, the temperatureallowed to recover, and 42 parts of Mg and 70 parts of Zn were added. Inthis case, 300 parts of lowed from this point. There was no indicationof any flame. The same series of treatments as above were given withthese respective Rockwell B hardness values: 47.3 t 12.8; 69.6 i- 7.0,69.9 i 9.8 and 71.3 :t 7.8.

EXAMPLE 14 A new alloy system was prepared by mixing 518 parts of Al and70 parts of Si and heating to 850C and maintaining for 1 hour. Then 42parts of Mg were added along with 70 parts of Zn. The usual procedurewas followed from that point including a C1 purge. Neither test specimenwas of any use.

The above was again repeated except all metallic ingredients were mixedat the beginning and no C1 purge was given. The as cast solution andtwo-stage precipitation (Rockwell E hardness) values were, in order:63.4 t 2.8; 77.6 i 6.4; 79.8 i 3.7; and 84.7 i 4.7.

The alloy compositions of Examples 7- 14 are summarized in Table llhereinafter.

E values of 95.3 i 3.2, 212 and 98.3 i- 2.1. 60

TABLE 11 Elements and Filler in Percent by Weight Al Mg Si Cu Fe Ti MnZn Zircon Alumina Exs. 7

and 8 39.0 3.9 13.0 2.6 6.5 35.0

Ex. 9 39.0 3.9 13.0 2.6 6.5 35.0 Ex. 10 42.0 4.2 14.0 2.8 7.0 30.0 .Ex.11 46.5. 4.0.. 12.51.. 1.3 0.5 w 0.1 0.1 0.1 35.0

ground zircon were added and the above procedure fol- TABLE ll-ContinuedElements and Filler in Percent by Weight Al Mg Si Cu Fe Ti Mn Zn ZirconAlumina Ex. l2 33.0 3.3 11.0 2.2 5.5 45.0 Ex. 13 42.0 4.2 14.0 2.8 7.030.00 Ex. l4 5L8 4.2 7.0 7.0 30.00

When the same ratio of components, with the exception of the magnesiumcontent, as was the case with Alloy A, was used as a basic alloy for afiller experiment, considerable experimental difficulties wereencountered and a very poor product was obtained.

The basic reason for the significantly harder than usual nature of AlloyA is the presence of crystalline silicon in a metal matrix. That alloycontains 17 percent silicon and the eutectic mixture for aluminum andsilicon is 11.7. Therefore, about one-third of the total silicon wouldcrystallize out on cooling and be dispersed in the metal matrix. In thecase of Alloy A there is no other component that would use up anysignificant amount of the excess silicon. When one adds sufficientamounts of magnesium to allow incorporation of the filler one has adifferent situation. Magnesium reacts with silicon to form theintermetallic Mg Si and thus significantly reduces the amount of Siwhich is free to crystallize out. Thus, one significantly reduces thehardness of the alloy. A new alloy was prepared that was designed tohave the same amount of silicon free to crystallize out after allowancewas made for the silicon removed as the magnesium-silicon intermetallic.This new alloy as cast was 85 percent as hard as Alloy A which may bedue to the presence of the intermetallic. After the 250F precipitationheat treatment to obtain the beneficial effects of the copper content,the hardness increased by 51 percent to 107 Brinell number which was 75percent of Alloy A value at that point. After the 350F precipitationheat treatment which was beneficial the Brinell number was 121, whichwas an increase of 12 percent over the previous value and 86 percent ofthe final Alloy A value.

Such an alloy produces an excellent metallic phase for a filled aluminumproduct.

There are very significant results contained in the foregoing examples.The Rockwell B hardness of 100.4 1*: 3.9 obtained in Example 8 is uniqueamong casting alloys whose value is considerably less in the majority ofcases and reaching higher values only in such special cases as the AlloyA engine alloy. Even wrought aluminum alloys do not generally reach thisvalue. Such a product is comparable with brass in hardness.

EXAMPLE 15 Following the procedure of Example 14 except that the alloysystem was held at 850C for 2 hours, a series of samples were made usingtwo types of zircon in percentages by weight percent of 42.0 Al; l4.0Si; 2.8 Cu; 7.0 Zn; 4.2 Mg; and 30.0 zircon. The samples were thentested for Brinell hardness after casting, solution heattreatment andfirst and second stage precipitation heattreatment. The results of thesetests are set forth in Table III as follows:

Tensile strengths of Alloy 2 with zircon were determined and the resultsare illustrated in Table [V as follows:

TABLE IV Yield Ultimate Strength Strength Percent Composite kpsi kpsiElongation Alloy 2 35% Zircon 3.6 13.5 5.3

EXAMPLE l7 Hardness and tensile strength of various alloys were comparedas a function of the level of zircon loading at various percentages from0 to 30 for alloys as follows:

Percent by Weight of Elements in Metallic Phase Alloy Al Mg Si Zn CuTABLE V Rockwell E Hardness Percent Zircon 0 l0 l5 20 25 30 Alloy 2 AsCast 89.6 85.0 36.2 75.6 92.] 96.4 After Solution Heat Treatment 83.959.4 71.5 70.7 80.3 85.8 After 250 Precipitation H.T. 97.8 88.3 87.783.8 93.6 91.5 After 350 H.T. 597* 09.5 81.9 831.3 59.7* 87.9

' Rockwell B Hardness TABLE VI Alloy 2 Similar tests using bismuth, amore effective metal at lowering surface tension, showed that bismuthwas not capable of reducing the filler surface and was completelyineffective in producing a satisfactory composite article. Other testsusing quartz as a filler indicated that the filler must be sufficientlystable so that it will not be reduced by the aluminum, but must bereduced by the metal reducing agent, namely magnesium.

The foregoing tests and other tests, showed that to obtain successfulresults at a 25-30 percent by weight filler level, there must beeffective stirring. The stirrer must also be in good condition andrun-at effective speeds. When contact times are on the order of 5minutes, a minimum of about 4 percent by weight of magnesium is requiredto product a satisfactory product. At a higher percentage of magnesiumloadings, the contact time may be shorter. Stirring or contact time andamount of filler go together. The degree of reduction of the filler isdetermined by the kinetics of the reduction which in turn is dependenton the concentration-time ratio.

Once the powdered filler was incorporated it showed little tendency toseparate by any mechanism other than Stokes law settling of theparticles. Settling is quite slow because of the smallness of thegrains, the high viscosity of the metallic phase and the extremesimilarity ofthe particle and melt density, especially with alumina asthe filler. Uniquely, no separaton of particles was observed when thefilled products were remelted and recast.

An increase in temperature of the mixture of about 20C was observed whenthe filler was added. This increase is due in part to stirring andchemical reaction.

Tin, which is an effective metal for reducing surface tension ofaluminum, would not provide the reducing action necessary for asuccessful product.

Hardness is a physical property that will have an effect on theuseability of the filled product as a replacement for otheraluminum-silicon casting alloys. The normal hardness range for suchcasting alloys is from a Brinell number of about 50 to a Brinell numberof about 120.

It may be seen that while there is a significant increase in hardnessbetween the basic aluminum-siliconmagnesium alloy and the same alloywith filler, i.e., a factor of about 2 with 25 percent alumina and about3 with 25 percent zircon, the best values obtained are still in thelower portion of the desired range.

Some control of the physical properties of the aluminum-siliconcomposite of this invention may be obtained by selection of anappropriate filler material. lf a tough cut or drill resistant compositeat some sacrifice of density is desired. zircon may be selected as afiller. If such properties are of less importance and low density isdesired, alumina would probably be selected as the filler.

The volume of the tiller in the metallic phase is the crucial factor indetermining the amount of filler that can be accepted by the metallicphase and still retain metallic like properties. The weight percent offiller that may be used is different for each filler and is dependentupon the filler density.

Intricate castings can be satisfactorily produced using the moltenfilled aluminum-silicon composite of this invention with little or noloss of desired physical properties as compared with a comparableunfilled aluminum-silicon alloy casting.

The foregoing disclosure and description of the invention isillustrative and explanatory thereof and various changes may be madewithin the scope of the appended claims without departing from thespirit of the invention.

What is claimed is:

l. A method of increasing the hardness of an aluminum-silicon composite,said composite consisting essentially of an aluminum, silicon, magnesiumalloy and a non-metal filler not subject to being reduced by aluminumselected from the group consisting of zircon, alumina, zirconia andaluminum silicates, said silicon being present in said alloy in anamount of 19-21 percent by weight said magnesium being present in saidalloy in an amount of about 2 to 10 percent by weight sufficient toreduce the surfaces of the non-metallic filler to a metal-like coatingwhen the metallic phase of the composite is in a liquid state, saidnon-metal filler constituting from about 5 to about percent of theweight of the composite, consisting essentially of subjecting saidcomposite to a threestage heat treatment as follows:

a. conducting a solution heat treatment at 800l ,000F for about 4 to 24hours followed by a quench; b. conducting a precipitation heat treatmentat 200300F for about 12 to 36 hours; and, c. conducting a secondprecipitation heat treatment at 300400F for about 4 to 12 hours. 2. Themethod of claim 1, wherein the non-metal filler has a particle size ofabout 60 mesh to about 400

1. A METHOD OF INCREASING THE HARDNESS OF AN ALUMINUMSILICON COMPOSITE,SAID COMPOSITE COMPRISING ESSENTIALLY OF AN ALUMINUM, SILICON, MAGNESIUMALLOY AND A NON-METAL FILLER NOT SUBJECT TO BEING REDUCED BY ALUMINUSELECTED FROM THE GROUP CONSISTING OF ZIRCON, ALUMINUM ZIRCONIA ANDALUMINUM SILICATES, SAID SILICON BEING PRESENTED IN SAID ALLOY IN ANAMOUNT OF 19-12 PERCENT BY WEIGHT SAID MAGNESIUM BEING PRESENT IN SAIDALLOY IN AN AMOUNT OF ABOUT 2 TO 10 PERCENT BY WEIGHT SUFFICIENT TOREDUCE THE SURFACE OF THE NON-METALLIC FILLER TO A METAL-LIKE COATINGWHEN THE METALLIC PHASE OF THE COMPOSITE IS IN A LIQUID STATE, SAIDNON-METAL FILLER CONSTITUTING FROM ABOUT 5 TO ABOUT 80 PERCENT OF THEWEIGHT OF THE COMPOSITE, CONSISTING ESSENTIALLY TIALLY OF SUBJECTING ANDCOMPOSITE TO A THREESTAGE HEAT TREATMENT AS FOLLOWS: A. CONDUCTING ASOLUTION HEAT TREATMENT AT 800*-1,000*F FOR ABOUT 4 TO 24 HOURS FOLLOWEDBY A QUENCH; B. CONDUCTING A PRECIPITATION HEAT TREATMENT AT 200*-300*FFOR ABOUT 12 TO 36 HOURS; AND, C. CONDUCTING A SECOND PRECIPITATION HEATTREATMENT AT 300*F-400*F FOR ABOUT 4 TO 12 HOURS.
 2. The method of claim1, wherein the non-metal filler has a particle size of about 60 mesh toabout -400 mesh, U.S. Sieve Series.